The present invention relates to a device and a method for controlling at least one operating-dynamics variable of a vehicle in closed loop. In particular, the present invention relates to a driving control of a braking system of the vehicle, and to the device utilized for this purpose.
Conventional devices and methods for controlling at least one operating-dynamics variable of a vehicle are known in numerous variations. For example, the publication xe2x80x9cFDRxe2x80x94Die Fahrdynamikregelung von Boschxe2x80x9d (FDRxe2x80x94Operating-Dynamics Control of Bosch), on pages 674-689 of the automobile technology periodical (ATZ) 96, 1994, issue 11, describes an exemplary conventional device and method. In this operating-dynamics control, a setpoint value is determined for the vehicle float angle and yaw rate, respectively, on the basis of at least the steering-wheel angle and the vehicular velocity. The setpoint values for the float angle and the yaw rate are supplied, together with the corresponding actual values, to a state controller which determines vehicle setpoint yawing moments from the corresponding system deviations. These vehicle setpoint yawing moments are converted, in view of the prevailing slip values, into setpoint slip changes at the suitable wheels. The setpoint slip changes are implemented by the subordinate ABS (antilock braking system) and ASR (traction control system) wheel-controller units. For example, when, during free rolling, the vehicle is oversteered in a right curve, and the setpoint yaw rate is exceeded, among other things, a setpoint brake slip is preset at the left front wheel, through which a yawing-moment change turning to the left acts on the vehicle, thereby reducing the overly great yaw rate. In the unbraked case, or when the driver initial pressure is not sufficient to adjust the desired setpoint slip, the pressure in the brake circuits is actively increased.
German Patent Application No. 40 35 527 (corresponding to U.S. Pat. No. 5,205,623) describes a hydraulic braking system having antilock braking system (ABS) and traction control system (ASR) for motor vehicles. This hydraulic conventional braking system features a hydraulic aggregate having at least one control valve and a return pump with at least one self-priming pump element which is operative in the brake circuit containing the at least one drive wheel. A valve arrangement, composed in each case of a charging valve and a selector valve, is used to make brake pressure available in ASR. The selector valve is arranged in the connection running from the master brake cylinder to the wheel brake cylinder of the drive wheel, and the charging valve is disposed in a suction line between the pump element and the brake-fluid reservoir. To achieve a hydraulic power requirement in ASR, the valve arrangement is driven in such a way that the selector valve blocks and the charging valve is opened for building up pressure, both valves block for holding pressure, and for reducing pressure, the charging valve blocks and the selector valve is opened.
With the above-described conventional devices and methods for controlling at least one operating-dynamics variable in closed loop (and the braking systems used in this context), in the event of a driver-independent brake-actuation as exists (e.g., during an ASR intervention), because of the driving of the circuit valves (i.e., the selector valve and the charging valve), pressure peaks can occur in a brake circuit while driving these valves due to the braking medium flowing into the brake circuit. These pressure peaks are not problematical in a large-volume design of the hydraulic aggregate. However, should a small-volume hydraulic aggregate be used, then greater pressure peaks can result due to the inflowing braking medium. These pressure peaks are disadvantageous for this hydraulic aggregate because of the great loading resulting from them.
One of the objects of the present invention is to provide a device and a method which make it possible to avoid high pressure peaks in the hydraulic aggregate in response to driver-independent braking interventions, thus reducing the loading of the hydraulic aggregate. Therefore, even small-volume hydraulic aggregates can be used.
The above-described pressure peaks, developing when carrying out a driver-independent braking intervention, are not problematical in large-volume hydraulic aggregates. However, should small-volume hydraulic aggregates be operated correspondingly, then the hydraulic aggregate must be driven by the appropriate controlling unit so that these pressure peaks do not occur, or occur only in reduced level. However, the full efficiency of the control is retained.
A braking system according to the present invention includes a reservoir for accommodating braking medium, and at least one brake circuit. The brake circuit contains first valve arrangements on the output side, and a second valve arrangement on the incoming side. Wheel brake cylinders allocated to the brake circuit are connected to the first valve arrangements. The reservoir is connected to the second valve arrangement. The first valve arrangement is composed in each case of a first and a second valve. The brake circuit further includes one pump. The second valve arrangement is composed in each case of a first valve, through which, in the flow-through (e.g., open) position, braking medium flows into the brake circuit in response to actuation of the pump, and of a second valve, through which, in the flow-through position, braking medium flows out of the brake circuit in response to actuation of the pump.
The device of the present invention includes means (e.g., an arrangement), with which the wheel brake cylinder exhibiting the greatest brake pressure is determined for the at least one brake circuit. During the time in which a driver-independent brake actuation exists, the first valve of the first valve arrangement is advantageously switched into the flow-through position, and the second valve of the first valve arrangement is switched into the blocking position for the wheel brake cylinder exhibiting the greatest brake pressure. Due to such driving control of the first valve arrangement, the pressure in the brake circuit corresponds to the pressure of the wheel brake cylinder exhibiting the greatest brake pressure. At the same time, the volume of the brake circuit is increased; thus possibly occurring pressure peaks cannot become all too large.
In response to a driver-independent brake actuation, in particular in response to a driver-independent build-up in brake pressure, the brake pressure of the wheel brake cylinder exhibiting the greatest brake pressure is advantageously adjusted by appropriate driving of the second valve arrangement. Due to this procedure, the first valve arrangement allocated to this wheel brake cylinder can remain in the above-described position. To adjust (in each case) the brake pressure of the remaining wheel brake cylinders of the brake circuit, the first valve arrangement allocated to the respective wheel brake cylinder is appropriately driven, in addition to the driving control of the second valve arrangement.
The first and second valve arrangements for the brake circuit are advantageously driven as follows. The respective volumetric requirement for the wheel brake cylinders allocated to the brake circuit is ascertained using appropriate means. In so doing, the respective volumetric requirement is advantageously ascertained at least as a function of the brake pressure which is adjusted in the respective wheel brake cylinder by the controlling unit on the basis of the setpoint selections. The sum of these volumetric requirements is ascertained on the basis of the individual volumetric requirements. By forming this sum, a measure is determined for ascertaining whether braking medium must be supplied to the brake circuit, or whether the braking medium must be removed from the brake circuit because of the driver-independent brake actuation. Since the second valve arrangement is composed of the xe2x80x9ccircuit valvesxe2x80x9d of the brake circuit which connect the brake circuit on the incoming side to the reservoir, and via which the braking medium can be carried into or out of the brake circuit, the second valve arrangement is advantageously driven as a function of the aforesaid sum. The first valve arrangements of the remaining wheel brake cylinders are driven in each case at least as a function of the volumetric requirement of the corresponding wheel brake cylinder.
The following is achieved for the brake circuit due to the above-described driving control of the first valve arrangements and of the second valve arrangement. Since the second valve arrangement is driven as a function of the sum of the individual volumetric requirements, only as much braking medium is fed to the brake circuit as is also necessary based on the requirement. Thus, no pressure peaks can develop. The same holds true for the removal of braking medium. The braking medium supplied via the second valve arrangement to the brake circuit is distributed to the remaining wheel brake cylinders according to their volumetric requirements by driving the first valve arrangements of the remaining wheel brake cylinders. Because the wheel brake cylinder exhibiting the greatest brake pressure is connected, by an appropriate interconnection (e.g., a switching arrangement) of the first valve arrangement allocated to it, to the brake circuit, the remaining wheel brake cylinders are also supplied by it (given appropriate pressure ratios). The resultant pressure losses in the wheel brake cylinder exhibiting the greatest brake pressure are compensated for by driving the second valve arrangement, into which the sum of the volumetric requirements enters.
The respective volumetric requirement of a wheel brake cylinder can be ascertained as a function of driving (trigger) times that are determined for actuating the first valve arrangement allocated to the respective wheel brake cylinder and/or as a function of the brake pressure prevailing in it at any one time, and/or as a function of a brake-pressure reference variable. In particular, the volumetric requirement is ascertained as a function of a difference determined between the brake pressure prevailing in the wheel brake cylinder and the brake-pressure reference variable.
As a function of the driving times, it is determined whether a brake-pressure build-up or a brake-pressure reduction exists for the wheel brake cylinder. For the brake-pressure reduction, a small predetermined value which can lie in the order of magnitude of, e.g., 0.4 bar is advantageously used as the brake-pressure reference variable. In the exemplary embodiment according to the present invention, this small value is definitively preset, however, it can also be adaptively determined. By using this small value, the respective volumetric requirement is first ascertained above this pressure value, resulting in an increase in the control precision, since, e.g., small fluctuations (particularly, sensor-contingent fluctuations) in an initial-pressure variable, which describes the initial pressure adjusted by the driver and which goes into the determination of the wheel brake cylinder pressures, are suppressed by this brake-pressure reference variable. The brake-pressure reference variable has the function of a threshold value. Consequently, a filtering is implemented by this procedure. If a brake-pressure buildup exists, a setpoint brake-pressure variable which describes the brake pressure to be adjusted in the appertaining wheel brake cylinder on the basis of the closed-loop control is selected as the brake-pressure reference variable. Therefore, for the brake-pressure buildup, the setpoint brake-pressure variable is selected as the brake-pressure reference variable, since the setpoint brake-pressure variable describes the brake pressure which is to be adjusted in the wheel brake cylinder on the basis of the actuation of the hydraulic aggregate.
With the determination of the difference determined between the brake pressure and the brake-pressure reference variable, and with the determination of the suitable driving times ascertained for actuating the respective first valve arrangements, it is possible to ascertain the respective volumetric requirement of the wheel brake cylinder. For the brake-pressure reduction, the volumetric requirement is advantageously ascertained using a first mathematical model, in particular, using physical relationships. For the brake-pressure build-up, the volumetric requirement is advantageously ascertained using a second mathematical model, in particular, evaluating a characteristics field as a function of the brake pressure.
The sum of the individual volumetric requirements is compared to a comparison value, in particular to a zero value. This comparison determines whether the braking medium must be supplied to the brake circuit, or whether the braking medium must be removed from the brake circuit. If this sum is greater than or equal to the comparison value, the first value of the second valve arrangement is driven as a function of this sum, and the second valve of the second valve arrangement is closed. If this sum is smaller than the comparison value, the first valve of the second valve arrangement is closed, and the second valve of the second valve arrangement is driven as a function of this sum.
It should be noted how the term volumetric requirement is to be understood in connection with the device and method according to the present invention. For the brake-pressure build-up, a positive volumetric requirement exists which indicates how much braking medium is to be supplied to the brake circuit. For the brake-pressure reduction, a negative volumetric requirement exists which indicates how much braking medium must be taken out or removed from the brake circuit.
The times for driving the first and the second valve of the second valve arrangement are advantageously ascertained as a function of a brake-circuit pressure variable which describes the brake pressure prevailing in the brake circuit, and as a function of the sum of the volumetric requirements. The driving time for the first valve is ascertained using a third mathematical model, preferably evaluating a characteristics field as a function of the brake-circuit pressure variable. The driving time for the second valve is ascertained using a fourth mathematical model, in particular using physical relationships.
The device according to the present invention further includes means (e.g., another arrangement) with which the number and/or the type of the brake-circuit wheel brake cylinders at which the brake pressure is increased is ascertained as a function of the driving times for the first valve arrangements. The number and/or the type of these wheel brake cylinders is taken into account in the driving of the first valve of the second valve arrangement. The type of the wheel brake cylinders is taken into account, since, for example, the wheel brake cylinders of the front axle have a larger volume than the wheel brake cylinders of the rear axle, and therefore exhibit different behavior in response to a brake-pressure build-up. The number of wheel brake cylinders is taken into account, since the brake circuit behaves differently in response to the brake-pressure build-up, depending upon the number of wheel brake cylinders at which the brake pressure is increased.